<script>
function load_content() {
    var invisible_doc = document.implementation.createHTMLDocument("");
    invisible_doc.body.innerHTML = '<html><body><form action="http://example.test:8080/security/resources/boring.html" method="post"></form></body></html>';
}

window.addEventListener("DOMContentLoaded", function listener() { load_content(); }, false);
</script>

<script>
window.onload = function() {
    if (window.opener)
        window.opener.postMessage('done', '*');
};
</script>
